1. Field of the Invention
The present invention relates to a method of sealing halogen lamp without using a tip tube.
2. Description of the Prior Art
FIG. 23 shows a conventional halogen lamp (B') having a typical configuration wherein sealing foils (10') are respectively embedded in seal portions (13') of a lamp envelop (1'), and the inner end of each sealing foil (10') is welded to a lead portion of a filament, while the outer end thereof is welded to a corresponding outer lead pin (11') extending to project outwardly from the seal portion (13').
It has been a conventional practice to seal this type of halogen lamps in the following manner. As shown in FIG. 22, an inert gas such as nitrogen or argon is supplied through a gas supply tube (20') connected to a tip tube (29') into the lamp envelop (1') and discharged from the opposite ends of the lamp envelop (1') to keep the inside of the envelop (1') in a non-oxidizing atmosphere. In this state, the opposite ends of the lamp envelop (1') are simultaneously or successively heated so as to be softened, and the end portions thus softened are pinch-sealed. Then, the gas within the lamp envelop (1') is sucked out through the tip tube (29') connected to the lamp envelop (1') to provide a high vacuum in the lamp envelop (1'). In turn, a required gas is filled into the lamp envelop (1'), and finally the tip tube (29') is cut-sealed at the base portion thereof by heating.
In this method, the inert gas is supplied into the lamp envelop (1') to retain the sealing foils (10') as well as the lamp envelop (1') in the non-oxidizing atmosphere so that the pinch-sealing can be achieved without oxidization of the surfaces of the sealing foils (10'). However, air sometimes enters the lamp envelop (1') instantaneously from the open ends thereof depending on the position of a burner or the intensity of flame, thereby causing the surface of the sealing foils (10') to be slightly oxidized. This results in poor adhesion between the lamp envelop (1') and the sealing foil (10') in the seal portions (13'), which leads to a high possibility of leak accidents of the product. Where a large amount of air enters the lamp envelop (1'), the surfaces of the sealing foil (10') are intensely oxidized and may be broken into fragments during the pinch-sealing. Further, where the outer lead pin (11') has a relatively small diameter, it may be burned out.
Further, even if the sealing foils (10') are not in an oxidized condition, the sealing foils (10') may be broken when applied with an increased pinching force greater than the breaking force in an attempt to enhance the adhesion between the seal portions (13') and the sealing foils (10'). Therefore, the relationship between the softening of the lamp envelop (1') and the pinching force is very delicate.
Furthermore, when the inert gas is supplied into the lamp envelop (1'), the gas flow causes the sealing foils (10') to flutter, hence, the position thereof to vary. Therefore, it is very difficult to pinch the lamp envelop (1') with the sealing foils (10') kept in predetermined positions within the seal portions (13'). Thus, a separate device is required for keeping the sealing foils (10') stationary.
Still further, the use of tip tube (29') results in a cut-sealed trace (30') of the tip tube (29') formed on a side surface of the lamp envelop, which not only renders the appearance of the lamp poor but also causes an internal strain to be left in peripheral portions thereof, decreasing the pressure resistance of the lamp envelop (1'). Repeating on/off operations of the lamp i.e., repeating heating and cooling of the lamp may eventually causes the lamp envelop to be broken from the cut-sealed trace (30').
Recently, halogen lamps adaptable for commercial voltages of less power consumption in many countries have been demanded. In response thereto, the volume of a lamp envelop can not help being decreased. However, if a tip tube is used in such a lamp envelop of a decreased volume, the lamp envelop can not be sufficiently cooled when it is immersed in liquid nitrogen for cutting the tip tube after a required gas is filled therein, because liquid nitrogen vaporizes due to the heat of a tip-off burner. As a result, the amount of the filling gas becomes insufficient and, hence, sufficient pressurizing of the lamp envelop can not be achieved. Thus, in spite of the recent tendency to increase the pressure of the gas to be filled in the lamp envelop so as to enhance the performance of the lamp such as a brightness and lifetime, the use of a tip tube makes it impossible to increase the filling gas pressure for such a small volume lamp envelop because of the reasons stated above. Further, the presence of the cut-sealed trace of the tip tube causes an internal strain to be left adjacent the trace and, hence, the lamp envelop can not endure such a high filling gas pressure. Consequently, it has been difficult to significantly enhance the performance of a small-sized halogen lamp of the type using a tip tube.
There exists another problem that the cut-sealed trace of the tip tube causes the scattering of light passing through the trace and the peripheral portion thereof, which leads to a decreased light-converging ability. Such a lamp is not suitable for use as a light source of high-precision apparatus such as a microscope or a measuring instrument.
It is, therefore, an object of the present invention to provide a novel method of sealing a halogen lamp, with which: the sealing foils are unlikely to be oxidized or broken; the outer lead pins are unlikely to burn out; a conventionally required tip tube can be dispensed with thereby providing a lamp envelop free of the cut-sealed trace; and the filling gas pressure can be increased.